Chemical synthesis of ammonia was successfully accomplished, by mass production, for the first time about 100 years ago by the German researchers Haber and Bosch. Haber-Bosch synthesis is the reaction represented by formula (1) below, and because it is simple and relatively efficient, it is still used in its same basic form even at the current time.N23H2→3NH3(about 400° C.)  (1)
Modifications to Haber-Bosch synthesis have been proposed in Patent document 1, for example, wherein the catalyst layer is separated into three layers, and heat exchange of reactive gas is carried out between each separated catalyst layer for intercooling, whereby the ammonia yield is increased based on equilibrium theory.
Conventionally, synthesis of ammonia from hydrogen and nitrogen has been accomplished using iron catalysts, but recently utilization of ruthenium-containing catalysts has been proposed for further reaction temperature reduction, so that increased ammonia yield can be achieved based on equilibrium theory.
The hydrogen used for synthesis of ammonia has conventionally been obtained using natural gas composed mainly of methane (CH4). Methane has a global warming potential of 23, where the global warming potential of carbon dioxide is defined as 1, and therefore leakage of natural gas during harvesting and use of natural gas composed mainly of methane has an adverse effect on global warming. Depletion of fossil fuels such as natural gas is also a serious issue. In addition, the use of natural as releases carbon dioxide as an essential combustion gas, and this also adversely affects global warming. It has therefore been proposed to obtain hydrogen by electrolysis of water, for synthesis of ammonia.
Patent document 2 relates to use of a ruthenium-containing catalyst for synthesis of ammonia from hydrogen and nitrogen, and to production of hydrogen for ammonia synthesis by electrolysis of water. The document teaches that ruthenium-containing catalysts are poisoned by water, carbon monoxide, oxygen and the like, and describes purification of the hydrogen and nitrogen used as starting materials for ammonia synthesis, in order to prevent such poisoning of ruthenium-containing catalysts. Specifically, Patent document 2 teaches that ruthenium-containing catalysts are poisoned by at least 1 ppm of trace oxygen, and at least 30 ppm of trace moisture, and trace carbon monoxide.
For purification of hydrogen and nitrogen as starting materials for ammonia synthesis, and particularly for removal of oxygen from hydrogen and nitrogen, Patent document 2 specifically proposes circulating a mixed gas of hydrogen and nitrogen through a reactor for removing trace oxygen (catalyst tube) packed with an oxidation catalyst, and thereby reacting the hydrogen and oxygen to produce water, and removing it.
Incidentally, in Patent document 3, there is proposed a method in which hydrogen is obtained by electrolysis of water and the hydrogen is passed through a metal oxide adsorption medium bed to remove impurities such as H2O, CO, CO2, O2 and hydrocarbons, in order to obtain high-purity ammonia to be used in a light emitting diode (LED) manufacturing process.